The RH antigens of human erythrocytes have been known for over 30 years. Their importance in iso-immune disease of the newborn and adult hemolytic anemia has become established. On the other hand, the chemical nature of these antigens remains very much in doubt. The reason for this is that these antigens have, thus far, not been obtained in free solution. The present evidence indicates that the antigenic structure is a combination of lipid and protein intimately linked with some membrane structure. This investigation is concerned with methods of attempting to solubilize these antigens and determine their chemical structure. The methods that are used in this investigation are the methods that have been devised to attempt to solubilize biological activity, such as enzymes, from membranes and other insoluble biological components. These includes detergents, and manipulations of pH, and ionic strength, etc. Evidence of antigen activity will be looked for in the solubilized supernatants by hemagglutination inhibition and other appropriate techniques. If evidence of activity is found, further characterization will be done.